1. Field of the Invention
The present invention relates to soil treatment by injecting or removing fluid, and certain embodiments relate to perforated casings that may be installed in the ground as a part of a soil remediation system. The perforated casings may be inserted into the soil without plugging openings in the casings. The perforated casings may be inserted into the soil without vapor or dust being transported from the soil to the surface through the casing.
2. Description of Related Art
Contamination of subsurface soils has become a matter of concern in many locations. Subsurface soil may become contaminated with chemical, biological, and/or radioactive contaminants. Contamination of subsurface soil may occur in a variety of ways. Hazardous material spills, leaking storage vessels, and landfill seepage of improperly disposed of materials are just a few examples of the many ways in which soil may become contaminated. Contaminants in subsurface soil can become public health hazards if the contaminants migrate into aquifers, into air, or into the food supply. Contaminants in subsurface soil may migrate into the food supply through bio-accumulation in various species that are part of the food chain.
There are many methods for removal of contaminants from subsurface soil. Some possible methods for treating contaminated subsurface soil include excavation followed by incineration, in situ vitrification, biological treatment, and in situ chemical treatment. Although these methods may be successfully applied in some applications, the methods can be very expensive. The methods may not be practical if many tons of soil must be treated.
Another method that may be used to remove contaminants from subsurface soil is a soil vapor extraction (SVE) process. An SVE process applies a vacuum to a production well to draw air through subsurface soil. The air carries volatile contaminants towards the source of the vacuum. Air, water, contaminants and other material may be removed as off-gas from the soil by the vacuum. The off-gas may be transported to a treatment facility. The off-gas removed from the soil may be processed in the treatment facility to eliminate or reduce contaminants within the off-gas to acceptable levels. An SVE process may allow contaminants to be removed from soil without the need to move or significantly disturb the soil. An SVE process may operate under roads, foundations, and other fixed structures.
In situ thermal desorption (ISTD) may be used to increase the effectiveness of an SVE process. An ISTD soil remediation process involves in situ heating of the contaminated soil to raise the temperature of the soil while simultaneously removing off-gas by vacuum. In situ heating may be preferred over convective heating by the introduction of a hot fluid (such as steam) into the soil because thermal conduction through soil is very uniform as compared to mass transfer through soil. Thermal conductivity of an average soil may vary by a factor of about two throughout the soil. Fluid flow conductivity of an average soil may vary by a factor of 108 throughout the soil.
Soil may be heated by a variety of methods. Methods for heating soil include, but are not limited to, heating by thermal conduction, heating by radio frequency heating, or heating by electrical soil resistivity heating. Thermal conduction heating may be advantageous because thermal conductive heating is not limited by the amount of water present in the soil. Also, soil temperatures substantially above the boiling point of water may be obtained using thermal conductive heating. Soil temperatures of about 212xc2x0 F., 250xc2x0 F., 300xc2x0 F., 400xc2x0 F., 750xc2x0 F., 1000xc2x0 F. or greater may be obtained using thermal conductive heating. Heaters may be placed in or on the soil to heat the soil. Thermal conductive heating of soil may include radiatively heating a well casing, which conductively heats the surrounding soil. Coincident or separate source vacuum may be applied to remove vapors from the soil. Vapor may be removed from the soil through production wells. U.S. Pat. No. 5,318,116 issued to Vinegar et al. and U.S. patent application Ser. No. 09/549,902, both of which are incorporated by reference as if fully set forth herein, describe ISTD processes for treating contaminated subsurface soil with thermal conductive heating.
A production well may be inserted into the soil. The production well may be placed, vibrated and/or driven into the soil. The production well may include a perforated casing that allows vapor to pass from the soil into the production well. The perforations in the casing may be, but are not limited to, holes and/or slots. The perforations may be screened. The casing may have several perforated zones at different positions along a length of the casing. When the casing is inserted into the soil, the perforated zones may be located adjacent to contaminated layers of soil. The areas adjacent to perforated sections of a casing may be packed with gravel or sand. The casing may be sealed to the soil adjacent to non-producing layers to inhibit migration of contaminants into uncontaminated soil.
In some soil remediation processes, it may be desirable to insert a fluid into the soil. The fluid may be, but is not limited to, a heat source such as steam, a solvent, a chemical reactant such as an oxidant, or a biological treatment carrier. A fluid, which may be a liquid or gas, may be inserted into the soil through an injection well. The injection well may include a perforated casing. The injection well may be similar to a production well except that fluid is inserted into the soil through perforations in the well casing instead of being removed from the soil through perforations in the well casing.
A well may also be a test well. A test well may be used as a gas sampling well to determine the location and concentration of contaminants within the soil. A different type of test well may be used as a logging observation well.
A production, injection or test well may be placed into an augered hole. Cuttings made during the formation of the augered hole may have to be treated separately from the remaining soil. Some soil may be contaminated with extremely toxic chemicals or radioactive contaminants. Augering a hole for a production or injection well may not be feasible because forming the hole would expose workers and the environment to contaminated dust or vapors. For example, soil may be contaminated with a combination of radioactive contaminants, such as plutonium, and organic contaminants. It may be desirable to remediate the soil to inhibit migration of the organic contaminants into adjacent soil. Exposure of workers to even small amounts of dust from plutonium contaminated soil during installation or operation of a soil remediation system may result in illness or death.
As an alternative to placing a production, injection or test well into an augered hole, a well may be inserted into the ground by vibrating or driving the well into the ground. U.S. Pat. No. 3,684,037 issued to Bodine and U.S. Pat. No. 6,039,508 issued to White describe devices for sonically drilling wells. Both of these patents are incorporated by reference as if fully set forth herein. During placement of a perforated casing into the ground, soil may fill and plug the openings in the casing. Plugged openings may inhibit or significantly reduce removal of off-gas from soil adjacent to the well.
A production, injection or test well for a soil remediation system may include a perforated casing. The casing may be an elongated conduit for introduction or removal of material into or out of the soil. The casing may have any cross sectional shape, including, but not limited to, circular, oval, polygonal, irregular, or rectangular. Perforations in the casing may be, but are not limited to, circular holes, oval holes, irregular shaped, and slots. The casing may be inserted into soil without the soil plugging openings of the perforated casing. In an embodiment, removable material may cover the openings during placement of the casing in soil. The removable material may inhibit openings in the casing from being partially or completely plugged by soil during the placement of the casing in the soil. The removable material may also inhibit transportation of dust and/or vapor through the casing during the placement of the casing into the soil. After the casing is placed into the soil the removable material may be removed by applying heat or chemical treatment to the removable material. The removable material may be removed by, but is not limited to being removed by, melting, vaporizing, dissolving, or reacting the material. The removable material may be a sleeve that is placed adjacent to the openings. Alternatively, the removable material may be plugs that are inserted or formed in each of the openings. In an alternate embodiment, openings in the casing may be oriented so that material is not packed into the openings during placement of the casing into the soil.
A removable material for plugging openings in a well casing may be, but is not limited to, a hydrocarbon, metal, metal alloy, plastic, polymer, or salt. Preferably, the removable material has good adhesion characteristics with the casing, has abrasion and melting point characteristics that allow the casing to be inserted into the ground without allowing the perforations to open, and has wetting characteristics with dry soil. The removable material should be non-toxic, and any breakdown products of the removable material should also be non-toxic. Good adhesion characteristics allow the removable material to form a seal with the casing to inhibit off-gas from escaping through the casing during placement of the casing into the soil. Contact between the casing and the soil may cause some of the removable material to abrade during placement of the casing into the soil. Good abrasion resistance characteristics may allow the casing to be placed into the soil without perforations of the casing becoming opened. During placement of a perforated casing into the soil, the temperature of the casing may increase due to vibration and friction with the soil. The melting point of the removable material and the size of the plug should allow the casing to be inserted into the soil without the perforations in the casing being opened. When the removable material is treated to open the perforations, a portion of the removable material or a breakdown product of the removable material may flow into the soil. Preferably, the removable material and/or the breakdown product has wetting characteristics with dry packing and/or soil adjacent to the well. The wetting characteristics may help to consolidate the packing and/or soil adjacent to the casing.
Openings in a casing of a well may be, but are not limited to, slots or holes. The openings may extend at an angle through a wall of the casing so that a low point of an opening in an outer surface of the casing is above a low point of the opening in an inner surface of the casing. In an embodiment, the openings in the casing are slanted outwards and upwards relative to the ground surface and an inner surface of the casing, and the openings of the casing are not covered during insertion of the casing into the ground. As the casing is placed into the ground, the slant of the openings inhibits material from being packed into the openings. In alternate embodiments, the openings in the casing are slanted outwards and upwards relative to an inner surface of the casing, and the openings of the casing are covered during insertion of the casing into the ground. The slant of the openings may allow material to flow into the casing if the removable material is removed by heating. The removable material may flow to a sealed bottom portion of the casing. In alternate embodiments, the openings have substantially no slant or an outward and downward slant relative to the ground surface and an inner surface of the casing. The un-slanted or downwardly slanted openings are covered during insertion of the casing into the ground to inhibit plugging and transmittal of dust and vapor to the atmosphere. Preferably, the removable material is vaporized or otherwise altered when the openings are exposed by heating or chemical treatment. The vaporization or alteration of the removable material may allow complete removal of the removable material from the casing and from soil adjacent to the casing.
In an embodiment, the removable material may be a hydrocarbon, metal, metal alloy, plastic, polymer, or salt that is dissolved by a chemical. The chemical may be, but is not limited to, an acid, a base, an oxidizer and/or a solvent. In other embodiments, steam or another fluid may be circulated within the casing to open the perforations in the casing after the casing has been installed in the ground.
Removable material may be placed in the perforations of a casing in a variety of ways. Individual plugs may be inserted into openings in the casing. The plugs may be held in place by a friction fit between the casing and the openings. The plugs may include flared ends that contact an inner surface of the casing and hold the plugs within the openings. The shape of the openings in the casing may help to retain the plugs within the casing. For example, the openings in the casing may have large areas in an outer surface of the casing. The openings may taper to smaller openings in an inner surface of the casing. The smaller openings at the inner surface of the casing may inhibit the plugs from being pushed into the casing during placement of the casing into the soil. Also, the plugs may tighten against the casing wall when a vacuum is pulled within the well. Alternately, the removable material may be melted, flowed into the openings, and allowed to harden. Excess removable material may be removed from the casing. The removable material may be a sleeve that is positioned against a surface of the casing. Preferably, the sleeve is placed and sealed to the outer surface of the casing, although in certain embodiments, the sleeve may be an inner lining placed against an inner surface of the casing.
A casing may include a screen or packing. In an embodiment, the casing may include a mesh screen. The mesh screen may have openings that are filled with a removable material during placement of the screen within the casing. In an alternate embodiment, the casing may include a wire wrap screen. The openings between the wraps may be filled with removable material. In addition to the openings in the screen, openings in a casing wall of a casing that has screen may also be filled with removable material. A casing may include packing. For example, a portion of the casing may be packed with sintered porous metal bead pack. The packing may be filled or blocked with removable material during installation of the casing into the ground.
In an embodiment, the material that forms the casing or a portion of the casing may be removable material. Such a casing may be fitted with a screen or a porous consolidated packing. For example, the casing may include or be a section of polyethylene pipe. A screen or packing may be placed within the pipe. After insertion of the pipe into the ground, the pipe or a portion of the pipe may be removed by melting and/or reacting the material of the pipe.
A production, injection or test well may be a pipe or pipe string that has a circular cross sectional shape. In some embodiments, the well may be a piling that has a rectangular or irregular cross sectional shape. U.S. Pat. No. 5,403,119 issued to Hoyle, and incorporated by reference as if fully set forth herein, describes production and injection wells that are pilings. A production or injection well that has a non-circular cross sectional shape may be driven into the ground by a pile driver, vibrated into the ground, or placed within a trench. An end of the piling may have a xe2x80x9cVxe2x80x9d shape to facilitate entry of the piling into the ground. The thickest part of the piling may be located in the xe2x80x9cVxe2x80x9d shaped end. As the piling is driven into the soil, the soil above the thickest portion of the xe2x80x9cVxe2x80x9d shaped end may rebound. The rebounding soil may provide a region of non-compacted soil adjacent to the piling.
A production, injection or test well that has a circular cross section shape may include an end that may be driven or vibrated into the soil. The end may be pointed to facilitate insertion of a well casing into the soil. In an embodiment of a casing that has a circular cross section, a maximum outer diameter of the end is larger than an outer diameter of the casing. The larger end may facilitate driving the well into the ground. As the end is driven into the soil, the opening created by the end will be larger than the outer diameter of the casing. As the casing is driven into the soil, the soil above the maximum diameter of the end may partially rebound. The rebounding soil may provide a region of non-compacted soil adjacent to the casing. In an alternate embodiment of a circular cross section shape casing with a pointed end, the end of the casing may have a maximum diameter that is substantially the same as the diameter of casing.
A perforated well casing may be placed in the ground in several ways, including, but not limited to, placing the well casing into an augered hole or trench, vibrating the well into the ground, or driving the well into the ground. A well casing having a circular cross sectional shape may be inserted into the ground by a combination vibratory and rotary driving system. The method used to insert a perforated well casing into the ground may be chosen based on several factors including, but not limited to, economics, type and toxicity of soil contamination at the remediation site, and soil formation properties.
A hole or trench may be formed in the ground for a well casing. A hole may be formed in the ground using an auger. The well casing may be placed into the hole. Several factors may be taken into account when placing well casings into augered holes or trenches within the ground. The cuttings produced during formation of the hole or trench may be treated separately. If the contamination is considered to be a hazardous waste, then the soil cuttings will also be a hazardous waste. The soil cuttings may require disposal or off-site treatment at an approved facility. Also, dust and or vapors may be generated during the formation of the augered hole or trench. Special dust and vapor containment procedures may be required which may make placement of the well casings into augered holes or trenches prohibitively expensive. Vibrating or driving a well casing into the ground may significantly reduce or eliminate dust and vapor generation during placement of the well casing into the ground.
Soil may include a number of layers. Removable material may be placed within a casing adjacent to selected layers of soil. The removable material may be removed from selected sections of the casing to independently and sequentially expose layers of the soil so that individual soil layers may be treated, injected into, or tested.
A perforated casing may be a component of a soil remediation system. In an embodiment, the soil remediation process is an in situ thermal desorption (ISTD) process. During an ISTD process, a heater is placed within the casing. Activating the heater heats the casing and the adjacent soil. The heater may be configured to heat the casing and the soil above a temperature that results in removal of removable material covering openings of the casing. The heater may be able to raise the temperature of the removable material to a temperature that opens the openings, but allows the temperature of the soil adjacent to the casing to remain below a temperature that results in migration of contaminants. When the openings are opened, a vacuum that pulls the contaminants and gas into the well may inhibit migration of contaminants. In an embodiment, the removable material and the heater may be chosen so that the heater raises the temperature of the casing and the soil to a working temperature that is sufficient to completely thermally destruct the removable material. In other embodiments, the removable material and the heater may be chosen so that the heater raises the temperature of the casing and the soil to a working temperature that is sufficient to result in the opening of the openings, but will not result in the thermal destruction of the removable material.
An advantage of a well casing that includes removable plugs or a removable sleeve over openings in the casing is that the casing may be inserted into the ground without plugging or partially plugging the openings in the casing during insertion of the casing into the soil. The removable plugs or sleeve may be dissolved by heating or chemical treatment after the casing is placed in the ground. After the plugs or sleeve are removed from the openings, off-gas may be removed from the soil through the casing if the casing is a part of a production well, or fluid may be injected into the soil through the casing if the casing is a part of an injection well.
Another advantage of a well casing that includes removable plugs or a removable sleeve over openings in the casing is that dust and/or vapor produced during an insertion procedure that places the casing in the ground will not be transported to the atmosphere through the casing. Preventing dust and vapor from passing through a casing during an insertion procedure may be critical for applications directed towards remediation of highly toxic contaminated soil. Highly toxic contaminated soils may include, but are not limited to, radioactive soils (such as plutonium contaminated soil), organic compound contaminated soil (such as dioxin contaminated soil), and/or mercury contaminated soil. Further advantages of well casings with removable plugs may include that the casings are sturdy, durable, simple, efficient, safe, reliable and inexpensive; yet the casings may also be easy to manufacture, install, and use.